On Thu, 15 Mar 2001, Ruud Baltissen wrote: > The only thing I can think of is that the author made the same mistake as I > did: assuming that the above 1 byte commands only take one cycle. Personal > remark: why do they need two??? Because the processor decodes the instruction opcode while fetching the second byte of the instruction. In the beginning of the 2nd cycle, it does not know whether it'll be a one-byte instruction or not. This greatly simplifies the design, I think. Another peculiarity is the JSR instruction. The high byte of the address is not read until the last (6th) cycle. If I remember correctly, also the return address pushed on the stack is incremented by one by the RTS instruction. Marko - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
Archive generated by hypermail 2.1.1.